es6的擴展運算符，箭頭函數，函數參數

1. 擴展運算符：

擴展運算符有以下四種：
        //展開數組
        let arr = [1,2,3,4];
        let a = [...arr];
        console.log(a);
            
        let b = [7,8,9,10];
        let g = [1,2,...b,4,5];
        console.log(g);
            
        //數組的拷貝
        let a = [1,2,3];
        let a1 = [...a];
        a1.push(4);
        console.log(a);
        console.log(a1);
            
        //數組的合併
        let a = [1,2,3];
        let a1 = [4,5,6];
        a = [...a,...a1];
        console.d(a);
            
        //數組的調用
        function  fn(a,b,c,d){
             console.log(a+b+c+d);
            }
            var p=[1,2,3,4,5,6];
            let result=fn(10,...p);

1. 箭頭函數：

        //箭頭函數
        let a = () => {
            console.log("Hello word")
        }
        a();
        //有參數
        (name)=>{
            console.log(name);
        };
        //沒有參數
        ()=>{
            console.log("hi word")
        };
        d('jiang');
        //兩個參數
        (name,age)=>{
            console.log(name,age);
        };
        //省略後的
        let c (a,b)=>a+b;
        (a,b)=>{console.log(a+b);
        console.log(c);
        //可以省略()
        let d = name=>{
            console.log(name);
        }
註釋：箭頭函數解決了定時器里的this指針問題。

1. 擴展參數(預設參數,擴展參數,剩餘函數)：

//預設參數
        let sayHellow = (name,age=30)=>{
            let str = `${name} is ${age} years old`
            console.log(str);
        }
        sayHellow("songze",25);//控制台列印songze is 25 years old。
        //擴展參數
        let sum = (a,b,c) => {
            console.log(a+b+c);
        };
        let arr = [1,2,3];
        sum(...arr);//控制台列印6。
        //剩餘函數
        let he = (a,b,...rest)=>{
        console.log(rest);//控制台列印[3, 4, 5, 6, 7, 8, 9]。
        console.log(a+b);//控制台列印3.
        }
        he(1,2,3,4,5,6,7,8,9);